Preparation of La_1−x K _x FeO₃ Microtubes and Their Adsorption Kinetics of Methyl Blue

The nanocrystalline La_1−x K _x FeO₃ (x ≤ 0.2) microtubes with a high specific surface area were prepared by the citrate-gel and thermal transformation process. These microtubes were characterized by X-ray diffraction (XRD), Brunauere–Emmette–Teller method (BET), and field emission scanning electron microscopy (FE-SEM). With the increase in K content (x) from 0 to 0.2, the average grain size decreases from 32.4 to 24.4 nm, and the specific surface area increases from 8.9 to 36.4 m²/g. The adsorption of methyl blue was analyzed by UV visible spectrophotometer. The adsorption capacity increases with the increase of the substituted-K content and the surface area of the La_1−x K _x FeO₃ microtubes. The adsorption results shows that all the La_1−x K _x FeO₃ microtubes exhibit a high adsorption activity for methyl blue, with the value of x ranging from 0 to 0.2, the adsorbance increases from 139.7 to 173.7 mg/g at the initial methyl blue concentration of 0.5 mg/mL in aqueous solution, and the kinetics data related to the adsorption of methyl blue onto the La_1−x K _x FeO₃ microtubes are in good agreement with the pseudo-second-order kinetic model in the initial methyl blue concentration of 0.1–0.5 mg/mL.